The technical field of the invention is a vehicle suspension control.
Many vehicles are provided with controlled suspensions in which dampers provide controlled damping of relative vertical body/wheel motion for vehicle wheels. The damping force of each controlled damper is determined by an electronic control signal provided by a controller derived from vehicle dynamic variables, typically including a signal from a relative body/wheel position sensor. Most of these dampers are provided with at least one bump stop device to cushion the damper when it is driven to its compression or extension limit; and it has been suggested that the damper controller can provide an electronically determined bump stop force by increasing damping force when the damper nears one of the compression and extension limit positions, as determined by the signal from the relative body/wheel position sensor. But build variations from vehicle to vehicle and from wheel to wheel may cause an offset between the position indicated by the sensor and the actual position of the damper relative to its compression and extension limits. This offset is generally irrelevant to the main control algorithm of the suspension controller, since the relative positions are typically only differentiated to obtain relative body/wheel velocities, with the offset disappearing in the differentiation. But incorporation of a bump stop algorithm in affordable, mass produced vehicles requires accurate relative body/wheel position relative to the damper compression and extension limits and thus typically requires the addition of a trimset compensation for each wheel to reference the output of the sensor to the compression and extension limit positions of the damper. A physical trimset adjustment is too costly to be practical in mass production.
This invention provides an accurate trimset of the relative body/wheel position sensor to the associated damper by receiving the sensor output with the body and wheel in a predetermined relative state and storing the received value as a reference or trimset value for use as an offset in deriving a damper position value from the relative position signal for each wheel. The damper position value is then used in a bump stop algorithm to accurately apply an increase in damping when the damper position is within a predetermined range of at least one of compression and rebound limit positions of the damper. Preferably, a scaled reduction in the increase of damping is provided as the damper position signal moves away from the compression or rebound limit position giving rise to the increase. In a preferred predetermined relative state of the body and wheel, the wheel is supported solely by the body through the suspension apparatus; and this state may be achieved for all the wheels of the vehicle by lifting the vehicle, for example on a hoist, until all wheels are off the ground. In an alternative relative state of the body and wheel, the body is supported by the wheel in the normal manner, although this embodiment is less preferred due to possible variations in body loading, especially in service trimset operations, that may affect the accuracy of the trimset value. In service trimset operations, the relative position value may be modified by a service offset value in deriving and/or storing the trimset value.